1. Field of the Invention
The invention relates to a data slicer, and more particularly, to a data slicer capable of calibrating charge and discharge current mismatch.
2. Description of the Prior Art
Digital data slicers, which compare analog signals with a reference level signal to determine whether the binary value of the input signal is “0” or “1”, i.e. to convert analog input signals into digital output signals, are widely used in transmission systems.
Please refer to FIG. 1 showing a block diagram of a conventional digital data slicer 100. The data slicer 100 has a comparator 110, an inverter 115, a charge pump 120, and a low pass filter 130. The charge pump includes a current source 121, a first switch 122, a second switch 123, and a current sink 124. In FIG. 1, the first switch 122 or the second switch 123 is turned on when the signal input to its control end is at high level respectively. When a sliced signal Vout is at high level, the first switch 122 is turned on and the second switch 123 is turned off, and the voltage source 121 charges node A. When the sliced signal Vout is at low level, the first switch 122 is turned off and the second switch 123 is turned on, and the current sink 124 discharges node A.
After processing voltage signals at node A with the low pass filter 130, a reference signal Vref is generated, and the comparator 110 can generate the sliced signal Vout by comparing an input signal Vin with the reference signal Vref. Theoretically, the current generated by the current source 121 or the current sink 124 must be the same in order to have a stable and accurate performance on data slicing.
However, it is very difficult to manufacture a current source 121 and a current sink 124 having the same charge or discharge current. Under the condition that there is a current mismatch between them, after a few periods, the error will be accumulated so that the whole system might become unstable and generate an erroneous sliced signal Vout. This is the main problem in the prior art.